tailieunhanh - An Introduction to Database Systems 8Ed - C J Date - Solutions Manual Episode 1 Part 2

Tham khảo tài liệu 'an introduction to database systems 8ed - c j date - solutions manual episode 1 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | An online application is an application whose purpose is to support an end user who is accessing the database from an online workstation or terminal. Persistent data is data whose lifetime typically exceeds that of individual application program executions. In other words it is data that a is stored in the database and b persists from the moment it is created until the moment it is explicitly destroyed. Nonpersistent data by contrast is typically destroyed implicitly when the application program that created it ceases execution or possibly even sooner. A property is some characteristic or feature possessed by some entity or some relationship . Examples are a person s name a part s weight a car s color or a contract s duration. By the way is a contract an entity or a relationship What do you think Justify your answer A query language is a language that supports the expression of high-level commands such as SELECT INSERT etc. to the DBMS. SQL is an example of such a language. Note Despite the name query languages typically support much more than just query . retrieval operations alone. Though not always OQL and XQuery see Chapter 25 and Chapter 27 respectively are examples of query languages that do support retrieval only. Redundancy means the very same piece of information say the fact that a certain employee is in a certain department is recorded more than once possibly in more than one way. Note that redundancy at the physical storage level is often desirable for performance reasons while redundancy at the logical user level is usually undesirable because it complicates the user interface among other things . But physical redundancy need not imply logical redundancy so long as the system provides an adequate degree of data independence. A relationship is an association among entities. Note As with entities it is strictly necessary to distinguish between relationship types and relationship occurrences or instances but in informal contexts we often use the same .

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